This research project aims at a better understanding of the molecular structure of sarcoplasmic reticulum membranes from muscle. This research is in the field of biophysics and uses primarily x-ray diffraction methods. Sarcoplasmic reticulum membrane fragments are isolated from muscle using the sucrose density gradient centrifugation. The isolated membranes are finally prepared as a multilayered array in the presence of excess fluid. X-ray diffraction experiments are carried out on these wet oriented membrane preparations. Sarcoplasmic reticulum membranes from a variety of different muscles are to be studied. The lamellar structure and the subunit structure will be studied. The structure analysis of the lamellar diffraction will provide an electron density description at right angles to the membrane surface. A structure analysis of the subunit diffraction will provide information on the size and arrangement of protein molecules in the surface of the membrane. The molecular distribution of the sarcoplasmic reticulum membranes will be studied after the completion of the structural analysis. It is anticipated that this research will contribute new information relating to the problem of muscle contraction.